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3*74         ON THE  CHANGE  OF  REFRANGIBILITY  OF  LIGHT.
the case of an extremely weak solution, as well as by the considerable degree in which the active rays were intercepted by glass, these rays, taken as a whole, must have been of very high refrangibility, such as to place them among the most refrangible of the fixed lines represented in the map, or perhaps even alto-o-ether beyond them. In making observations on the solar spectrum, it was plain that the prisms were by no means transparent with respect to the rays belonging to the group p of fixed lines. Yet these rays, before they produced their effect, had to pass twice through the plate-glass belonging to the mirror (except so far as regards the rays reflected at the first surface), then through three prisms, though to be sure as close us possible to the edges, then through a lens by no means very thin, and lastly, through the side of the vessel containing the fluid. Such a train of glass would be sufficient materially to weaken, if not even wholly to cut off the active rays coming from the flame of a spirit-lamp.
200. The flame of naphtha* produces nearly the same effect as that of alcohol. The flame of ether is not so #ood ; but whether this arises solely from its richness in visible rays, which only produce a glare, or likewise from a comparative poverty in highly refrangible invisible rays, it is not easy to say. The ilame of hydrogen produces a very strong effect. Tin* invisible rays in which it so much abounds, taken as a whole, appear to be even more refrangible than those which eoine from the ilamo of a spirit-lamp. In making some observations with the tlaine of hydrogen, when the gas was nearly exhausted, so that the {lame was reduced to a roundish knob no larger than a, sweet pea, and giving hardly any light, it was found still to produce a very marked effect when held over the surface of a solution of sulphate of quinine. The flame of sulphuret of carbon produces on most objects a much stronger effect than that of alcohol. It exhibits distinctly the blue light dispersed close.', to the surface, of a solution of guaiacum in alcohol, which the flame of alcohol does not. It appears then that the flame of sulphuret of carbon is rich in invisible rays of such a refrangibility as to place them among the groups of fixed lines m, n, or a little beyond, since
[* By this was meant wood-spirit, commercially culled miphtha, nut the hydrocarbon to which the name more properly belongs.]